The Jackson Laboratory is a private not-for-profit research organization incorporated under the laws of the state of Maine since 1929. The work of the Laboratory spans three overlapping areas: research, resource and training. The Research Animal Facility benefits all of these areas by providing high quality animal care and competent technical assistance to investigators, trainees and resource personnel. Laboratory Animal Medicine programs provide comprehensive veterinary, diagnostic and monitoring activities. In addition, Genetic Quality Control monitors the genetic integrity of Jackson Laboratory mice. The aim of this proposal is to upgrade the Research Animal Facility by the addition of 22 units of pressurized, individually ventilated (PIV) caging - complete with polycarbonate cages, stainless steel covers, bottles and filter/blower modules - and 4 mobile HEPA filtered change stations. These units are required by investigators who are using immunodeficient mice in their research programs. These heritable immunological defects in mice are excellent models for immunodeficiency and autoimmunity disease in man, but research is often hampered by the fact that these animals are susceptible to infection by opportunistic microorganisms, even when housed under the exceptionally clean conditions prevailing in the Research Animal Facility. In order to collect accurate data and generate reproducible results, these investigators must be confident that the immunological responses under investigation are not the result of opportunistic infection. The addition of PIV caging will address this problem and help achieve the goal of the Research Animal Facility to provide all investigators with the highest quality animal care possible.